1. Field of the Invention
This invention relates to Multimedia Broadcast/Multicast Service (hereinafter referred to as MBMS), and in particular to Method or creating and assigning Temporary Moving Group Identifier (TMGI).
2. Description of the Prior Art
MBMS is a new service under standardization by 3rd Generation Partnership Project (simplified as 3GPP). MBMS service is an unidirectional point-to-multipoint (p-t-m) service, whose most remarkable characteristic is that it can make use of radio resources and network resources efficiently. In this service, multimedia data sent from data source are transferred to a plurality of users via transmission network. This kind of p-t-m service can save network resources. MBMS service is mainly used in radio communication network system, e.g. Wideband Code Division Multiple Access (hereinafter referred to as WCDMA), Global System of Mobile Communication (hereinafter referred to as GSM), etc. MBMS data transmission basically includes following steps: data source transmission, middle network transmission, destination cell on-the-air transmission and user receiving. FIG. 1 is the logical figure for network devices that can provide MBMS service, in which MBMS actually makes use of General Packet Radio Service (hereinafter referred to as GPRS) as core transmission network. As shown in FIG. 1, Broadcast/Multicast Service Centre (hereinafter referred to as BM-SC) is the data source for MBMS data transmission; Gateway GPRS Supporting Node (hereinafter referred to as GGSN) is used to connect GRPS network with external network, such as INTERNET, which is used to connect BM-SC in MBMS service and to send MBMS data to specific Service GPRS Supporting Node (hereinafter referred to as SGSN); Cell Broadcast Centre (hereinafter referred to as CBC) is the data resource of cell broadcast. Through interconnecting CBC with BM-SC in MBMS, CBC can provide MBMS service announcement function; SGSN is used to perform access control on UE as well as mobility management, and sends MBMS data from GGSN to specific Radio Network Controller (hereinafter referred to as RNC) at the same time; RNC is used to control a group of base stations (hereinafter referred to as NODE B) and sends multimedia data to specific NODE B; NODE B (base station) establishes air physical channel for MBMS service in a certain cell under the control of RNC; Terminal User Equipment (hereinafter referred to as UE) is the terminal equipment for MBMS data reception.
FIG. 2 gives the whole process from service announcement, joining, service notification, and radio bearer set up till user's final leaving in MBMS service.
000 Subscription—setting up the connection between user and service provider, and authorizing user to receive relevant MBMS service.
001 Service announcement—notifying user of services to be provided. For example, the system will rebroadcast-a football match in Beijing at 7:00 p.m.
002 Joining—indicating that user joins a group, i.e. the user informs the network that he or she is willing to receive this multicast service.
003 MBMS multicast mode bearer set up—setting up network resources for MBMS data transfer.
004 MBMS notification—notifying user of MBMS data transfer to be performed immediately.
005 Data transfer—indicating the process of transferring MBMS service data to user.
006 MBMS multicast mode bearer release—indicating the releasing of network resources after MBMS service data transfer finishes.
007 leaving—corresponding to 002 joining, which indicates that a user is leaving a group, i.e. the user doesn't want to receive the data of a certain service any more.
As MBMS service is provided to a plurality of users simultaneously, a paging block is easy to happen during the process of MBMS notification. A Temporary Moving Group Identifier (hereinafter referred to as TMGI) is assigned to users of the same group, which can solve the deficiency of one-by-one paging for a plurality of users at the same time. TMGI is assigned by SGSN. Before MBMS data transfer, TMGI is transferred to UE via GPRS attach, routing area update or group division—Packet-Temporary Moving Subscriber Identifier (hereinafter referred to as P-TMSI) re-assignment process. The first assignment shall be performed when user joins the MBMS service. Different multicast service has different TMGI identifier in the same SGSN. TMGI can prevent from paging block on radio interface.
An Iu-Flex is the new interface between RNC and core network (hereinafter referred to as CN). The Iu-Flex is introduced to effectively make use of network hardware resources and to reduce signaling interaction due to location update. When applied into MBMS system, as shown in FIG. 5, a RNC connects with a plurality of SGSNs at the same time. And the serving SGSNs of UE1, UE2 and UE3 are different. As the serving SGSN of UE 1 is SGSN1 and that of UE2 and UE3 is SGSN2, MBMS data source of UE1 is different from that of UE2 and UE3. In the situation of MBMS notification, two SGSNs send MBMS paging message to RNC simultaneously A plurality of SGSNs shall assign the same TMGI for the same MBMS service so that RNC can detect that a plurality of MBMS notifications are for the same MBMS service. Besides TMGI, IP multicast address can also be used to notify RNC that multiple MBMS notifications sent from SGSN are for the same service. IP multicast address is told to UE during the period of service announcement or service discovery.
TMGI is assigned by SGSN, and SGSN doesn't know the TMGI assigned by other SGSN for this service. If a plurality of SGSNs assign different TMGIs for the same service, RNC needs to send a plurality of copies of paging for the same service when the plurality of MBMS notifications are sent to different users in the same RNC. This may not only result in waste of resources but also result in confusion at RNC. Accordingly, when Iu-Flex exists, it is improper to assign TMGI by SGSN and it is difficult to guarantee that the plurality of SGSNs may assign the same TMGI for the same service. If RNC uses IP multicast address and service is not distinguished by TMGI, the above problem can be solved, but which makes it necessary for paging message to carry TIP address when RNC sends paging to user. IPv6 address has 128 bits, which results in additional overheads when it is transmitted on air interface. If IP address is really adopted as paging identifier, it means that the paging identifier is consistent all over the world, which is unnecessary and results in management confusion.